Usually a light emission device based on LEDs (the acronym for light emitting diodes) consists of a stack of semiconductor layers produced by epitaxy on a sapphire or silicon carbide (SiC) substrate having a mesh parameter suited to the material of the semiconductor layers. A plurality of diodes is usually simultaneously produced to the scale of a wafer, and then the diodes are individualised by cutting. The single chips thus obtained are then attached, according to the application, to a supporting substrate known as a PCB (printed circuit board) of a light system for electrical supply thereof, the number of chips attached to the PCB being chosen according to the brightness required for the lighting system.
The manufacture of this type of LED, however, remains complex and expensive since it requires very many steps, in particular steps of thinning and/or shrinkage of the epitaxial growth substrate and, where applicable, a step of attaching the LEDs to a PCB.
But especially, an important proportion (approximately 80%) of the electrical energy injected into such LEDs is converted into heat. In doing this, not only is the efficiency of such diodes low, but the service life thereof is substantially shortened if they suffer significant heating. Problems of thermal dissipation are thus posed, all the more so when a high brightness of the lighting system, and therefore a large number of diodes, is required. In fact, thermal dissipation remains the main reason why this type of LED does not become more widespread.
The electrical supply to an LED is usually limited to a few watts in order to avoid heating thereof to temperatures above 150° C. and/or active diode cooling devices (fan, Peltier effect module, etc.) are provided in the lighting system.
In order to reduce the thermal resistances opposing good dissipation of heat (in particular, the high thermal resistance of the layers for holding the LEDs on a board), the LEDs can also be directly integrated on the board (then “chip on board” is spoken of), which eliminates the thermal resistances related to the transfer. However, the integration operations are complex and the gain in thermal dissipation insufficient.
Recently LEDs based on nanowires have appeared, the advantage of which is not requiring a match in mesh between the material constituting an LED and the nanowire growth substrate. A wide choice of substrate is thus possible, not only sapphire and SiC, and in particular, substrates affording good thermal dissipation of the heat produced by the LED, such as for example metals. Reference can for example be made to the document WO 2007/141333 for a detailed description of the manufacture of such an LED.
Although the number of manufacturing steps is more limited, because in particular of the substrate, which is not removed, the LEDs are still produced simultaneously and then individualised and the individualised LEDs attached to a PCB or integrated directly on a board. In fact, the steps of constructing a lighting system are still numerous and the transfer of the LEDs onto a PCB or integration thereof on a board causes numerous thermal resistances reducing the efficacy of the heat dissipation.